kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 173 insertions, 0 deletions

diff --git a/drivers/hid/hid-gaff.c b/drivers/hid/hid-gaff.c
new file mode 100644
index 000000000..8b99686b6
--- /dev/null
+++ b/drivers/hid/hid-gaff.c
@@ -0,0 +1,173 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Force feedback support for GreenAsia (Product ID 0x12) based devices
+ *
+ *  The devices are distributed under various names and the same USB device ID
+ *  can be used in many game controllers.
+ *
+ *  0e8f:0012 "GreenAsia Inc.    USB Joystick     "
+ *   - tested with MANTA Warior MM816 and SpeedLink Strike2 SL-6635.
+ *
+ *  Copyright (c) 2008 Lukasz Lubojanski <lukasz@lubojanski.info>
+ */
+
+/*
+ */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+#include "hid-ids.h"
+
+#ifdef CONFIG_GREENASIA_FF
+
+struct gaff_device {
+	struct hid_report *report;
+};
+
+static int hid_gaff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct gaff_device *gaff = data;
+	int left, right;
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+
+	dbg_hid("called with 0x%04x 0x%04x", left, right);
+
+	left = left * 0xfe / 0xffff;
+	right = right * 0xfe / 0xffff;
+
+	gaff->report->field[0]->value[0] = 0x51;
+	gaff->report->field[0]->value[1] = 0x0;
+	gaff->report->field[0]->value[2] = right;
+	gaff->report->field[0]->value[3] = 0;
+	gaff->report->field[0]->value[4] = left;
+	gaff->report->field[0]->value[5] = 0;
+	dbg_hid("running with 0x%02x 0x%02x", left, right);
+	hid_hw_request(hid, gaff->report, HID_REQ_SET_REPORT);
+
+	gaff->report->field[0]->value[0] = 0xfa;
+	gaff->report->field[0]->value[1] = 0xfe;
+	gaff->report->field[0]->value[2] = 0x0;
+	gaff->report->field[0]->value[4] = 0x0;
+
+	hid_hw_request(hid, gaff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int gaff_init(struct hid_device *hid)
+{
+	struct gaff_device *gaff;
+	struct hid_report *report;
+	struct hid_input *hidinput;
+	struct list_head *report_list =
+			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct list_head *report_ptr = report_list;
+	struct input_dev *dev;
+	int error;
+
+	if (list_empty(&hid->inputs)) {
+		hid_err(hid, "no inputs found\n");
+		return -ENODEV;
+	}
+	hidinput = list_entry(hid->inputs.next, struct hid_input, list);
+	dev = hidinput->input;
+
+	if (list_empty(report_list)) {
+		hid_err(hid, "no output reports found\n");
+		return -ENODEV;
+	}
+
+	report_ptr = report_ptr->next;
+
+	report = list_entry(report_ptr, struct hid_report, list);
+	if (report->maxfield < 1) {
+		hid_err(hid, "no fields in the report\n");
+		return -ENODEV;
+	}
+
+	if (report->field[0]->report_count < 6) {
+		hid_err(hid, "not enough values in the field\n");
+		return -ENODEV;
+	}
+
+	gaff = kzalloc_obj(struct gaff_device);
+	if (!gaff)
+		return -ENOMEM;
+
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	error = input_ff_create_memless(dev, gaff, hid_gaff_play);
+	if (error) {
+		kfree(gaff);
+		return error;
+	}
+
+	gaff->report = report;
+	gaff->report->field[0]->value[0] = 0x51;
+	gaff->report->field[0]->value[1] = 0x00;
+	gaff->report->field[0]->value[2] = 0x00;
+	gaff->report->field[0]->value[3] = 0x00;
+	hid_hw_request(hid, gaff->report, HID_REQ_SET_REPORT);
+
+	gaff->report->field[0]->value[0] = 0xfa;
+	gaff->report->field[0]->value[1] = 0xfe;
+
+	hid_hw_request(hid, gaff->report, HID_REQ_SET_REPORT);
+
+	hid_info(hid, "Force Feedback for GreenAsia 0x12 devices by Lukasz Lubojanski <lukasz@lubojanski.info>\n");
+
+	return 0;
+}
+#else
+static inline int gaff_init(struct hid_device *hdev)
+{
+	return 0;
+}
+#endif
+
+static int ga_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret;
+
+	dev_dbg(&hdev->dev, "Greenasia HID hardware probe...");
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed\n");
+		goto err;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT & ~HID_CONNECT_FF);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		goto err;
+	}
+
+	gaff_init(hdev);
+
+	return 0;
+err:
+	return ret;
+}
+
+static const struct hid_device_id ga_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_GREENASIA, 0x0012),  },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ga_devices);
+
+static struct hid_driver ga_driver = {
+	.name = "greenasia",
+	.id_table = ga_devices,
+	.probe = ga_probe,
+};
+module_hid_driver(ga_driver);
+
+MODULE_DESCRIPTION("Force feedback support for GreenAsia (Product ID 0x12) based devices");
+MODULE_LICENSE("GPL");